This invention relates to a method of, and a patella clamp and reamer with an adjustable stop for, in situ preparation of a patella.
During certain forms of surgery involving the knee, such as the implantation of a knee joint prosthesis, the natural patella is resected for subsequent implantation of an artificial patella component. During such a resection, various parameters must be considered in determining the desired depth of the resection. For example, the surgeon must consider the thickness of the natural patella as well as the thickness of the artificial patella components which will be implanted. In addition, the artificial patella component is typically available in different diameters so as to give the surgeon flexibility in operating on natural patellas of different sizes. However, an increase in the diameter of the artificial patella component normally results in a corresponding increase in the thickness of the artificial patella component. It is therefore often difficult for a surgeon to easily determine the depth to which a natural patella must be resected when having to consider all of these factors.
Once the surgeon has determined how much the natural patella should be resected, the patella is clamped so as to hold the patella in the fixed position. Various devices have been developed which allow the surgeon to hold the patella stationary. These devices typically involve hand operated scissors and vise-grip mechanisms. However, these devices suffer from the fact that the surgeon must maintain a clamping pressure on the patella. This application of clamping pressure may not be uniform during the resection of the patella, and possibly result in the patella being malpositioned. Accordingly, in some of the known constructions, gimbals are necessary in the jaws of such instruments to accurately position the patella during the resection procedure. Finally, some of these devices, such as the four-bar clamp which is available from Biomet, are large and bulky and therefore difficult to use and do not provide a relatively high degree of tactile feedback.
In addition, presently available instruments move a guide bushing into position against the posterior surface of the patella to clamp the patella and guide the reamer. This obscures the view of the patella such that the surgeon cannot see the patella during the resection process. This arrangement also tends to generate wear debris because the cutting blade assembly tends to contact the guide bushing.